Grinding is an important machining process of finish machining, the machining procedure thereof is to use a grinding wheel to interact with a workpiece, and since abrasive particles on the surface of the grinding wheel generally cut at negative rake angles, heat generated in the grinding procedure is much larger than that in other machining forms. When grinding the workpiece material, a large amount of mechanical energy consumed by the abrasive particles is converted into heat, only a small part of the heat on a grinding interface is taken away by a grinding shoulder, more than 90% of the heat is transferred to bodies of the grinding wheel and the workpiece, thereby generating serious influence on the service life of the grinding wheel and the use performance of the workpiece. Due to the grinding high temperature, the surface layers of the abrasive particles on the surface of the grinding wheel are weakened, and the abrasion is worsened, resulting in abrasive particle deviation and other phenomena and shortening the service life of the grinding wheel. When a large number of grinding heat is transferred to the workpiece, residual stress is formed on the surface layer very easily, and even cracks and other phenomena are generated on the surface, which influence the size precision and shape precision of the workpiece, when the temperature reaches a certain limit, the surface of the workpiece is subjected to grinding burn, and a metallographic structure on the surface layer of the workpiece is more likely to change, thereby seriously influencing the fatigue resistance and wear resistance of the workpiece, and reducing the usability and reliability of the workpiece. If the heat on the grinding interface cannot be dissipated in time, heat damage is generated easily.
Minimal quantity lubrication grinding is a green machining technology, it refers to a grinding technology in which an extremely small amount of lubrication fluid is mixed and atomized with a gas having a certain pressure, and then the mixture is jet to a grinding area for cooling and lubrication, and the cooling and chip removal functions are mainly realized by a high pressure gas. 30-100 ml of grinding fluid is adopted on a unit grinding wheel width of minimal quantity lubrication grinding, while 60 L/h of grinding fluid is adopted in pouring grinding; but minimal quantity lubrication reaches and even exceeds the pouring grinding effect, and meanwhile, the consumption of the grinding fluid is greatly reduced. Nanoparticle jet flow minimal quantity lubrication refers to adding a certain amount of nano solid particles in degradable minimal quantity lubrication oil on the basis of the minimal quantity lubrication to form nanofluid, atomizing the nanofluid though high pressure air and conveying the nanofluid into the grinding area in a jet flow manner. It can be seen from the enhanced heat transfer theory that, the heat transfer ability of solid is much larger than that of liquid and gas. The heat conductivity of a solid material at the normal temperature is larger than that of a fluid material for several orders of magnitudes, and the heat conductivity of liquid with suspended metal, non-metal or polymer solid particles is much larger than that of pure liquid. If the solid particles are added in a minimal quantity lubrication medium, the heat conductivity of the fluid medium can be greatly enhanced, the convective heat transfer ability can be improved and the defects of insufficient minimal quantity lubrication cooling ability can be greatly compensated. In addition, the nanoparticles (refer to ultrafine tiny solid particles having at least one dimension located in a nanometer scale (1-100 nm) in a three-dimensional space) further have special anti-wear antifriction and high carrying capacity and other tribological properties on lubrication and tribological aspects. The nano solid particles are added in the minimal quantity lubrication fluid medium to form the nanofluid, namely, the nanoparticles, lubrication liquid (oil, or oil-water mixture) and the high pressure gas mixture are jet into the grinding area in the jet flow manner after being mixed and atomized. The nanoparticle jet flow minimal quantity lubrication grinding is to provide a novel grinding process having the advantages of the minimal quantity lubrication technology and having stronger cooling performance and excellent tribological properties, and special equipment for realizing the process, the grinding burn can be effectively solved, the surface integrity of the workpiece can be improved, and low-carbon green and clean production with high efficiency, low consumption, environment friendliness and resource saving can be realized.
An electrocaloric effect is also called a thermoelectric effect, which changes the polarized state of a polar material under the action of an external electric field to generate an adiabatic temperature change or an isothermal change. The basic idea of the electrocaloric effect is to change the polarized state of the material under the action of the external electric field to change an entropy, so as to enable the material generate the temperature change. Therefore, the temperature can be regulated and controlled by changing the polarized state of the material through the external electric field, so as to realize refrigeration. The basic principle of refrigeration of the electrocaloric effect is to apply the electric field to the polar material, electric dipoles in the material become orderly from disorderly, the entropy of the material is reduced, and under an adiabatic condition, the excessive entropy generates temperature rise. If the electric field is removed, the electric dipoles in the material become disorderly from orderly, the entropy of the material is increased, and under an isothermal condition, the material absorbs heat from the outside to ensure energy conservation. Or, under the adiabatic condition, insufficient entropy causes temperature drop of the material, and the whole procedure is similar to a Carnot cycle. For an ideal refrigeration cycle, when the electric field is removed, the electrocaloric material can absorb heat (isothermal entropy) from a load in contact therewith. Then, the electrocaloric material is separated from the load, and at this time, the electric field is applied to the electrocaloric material, the temperature of the material will rise (adiabatic temperature change). The electrocaloric material is in contact with a cooling fin, and the excessive heat will be released, so that the temperature of the electrocaloric material is consistent with the room temperature. Then, the electrocaloric material is disconnected from the cooling fin and is in contact with the load. When the electric field is removed, the temperature of the electrocaloric material drops and the electrocaloric material absorbs heat from the load. The whole procedure is repeated, the temperature of the load will continuously drop. This is the basic principle of an electrocaloric refrigerator. At present, the electrocaloric refrigeration is widely used in micro electro mechanical systems (MEMS), and the electrocaloric refrigeration has the advantages of being simple in structure, free of mechanical moving parts, small in volume, especially suitable for partial cooling, high in startup speed, flexible to control, free of mechanical compression, high in refrigeration efficiency, low in cost, free of compressed gas or refrigerant and harmless to the environment, so that the electrocaloric refrigeration is a novel refrigeration technology having a brilliant development prospect.
Among numerous heat transfer elements, a heat pipe is one of the most efficient heat transfer elements known to people at present, it can rely on the phase change of its own internal working fluid to transmit a large amount of heat at a long distance through a very small sectional area without additional power. The so-called heat pipe grinding wheel refers to forming a heat pipe structure and function in a grinding wheel body by an appropriate method, so as to greatly improve the heat conductivity of the grinding wheel compared with that of the traditional common grinding wheel, and the heat of the cambered grinding area can be directly introduced into a heat pipe evaporation end and quickly dispersed by the heat transfer function of the heat pipe, so as to reduce the heat accumulation in the cambered grinding area and reduce the grinding temperature to avoid workpiece burn when efficient grinding is carried out on the workpiece material.
The Chinese Patent CN2013106349914 discloses nanoparticle jet flow controllable transport minimal quantity lubrication grinding equipment in a magnetically enhanced electric field, and a magnetic field is added around a corona area to improve the charge quantity of droplets; a high-voltage DC electrostatic generator and a nozzle of a magnetic field forming device are arranged at the outside of the equipment; the nozzle is connected with a nanoparticle liquid supply system and a gas supply system; the high-voltage DC electrostatic generator is connected with a negative electrode of an adjustable high-voltage DC power supply, and a positive electrode of the adjustable high-voltage DC power supply is connected with a workpiece energizing device attached to a non-machined surface of the workpiece to form a negative corona discharge form; the magnetic field forming device is arranged around the corona area of electrostatic discharge; when the grinding fluid is jet out from a spray head of the nozzle and is atomized to droplets, the droplets are charged under the action of the high-voltage DC electrostatic generator and the magnetic field forming device to convey the nanofluid into the grinding area. The electrostatic atomization nozzle adopted by the equipment is an integrated nozzle, which is relatively complex to machine and cannot be combined with other equipment, thereby requiring further improvement and optimization.
The Chinese patent CN200410009666.X discloses a micro refrigerator and a refrigeration method thereof, and particularly relates to a ferroelectric stack array micro refrigerator and a refrigeration method thereof. A relaxor ferroelectric material is used as a refrigerant, and the micro refrigerator is composed of n layers of ferroelectric stacks, m×1 ferroelectric stack arrays and n×m×1 unit refrigeration sheets in total; each refrigeration sheet adopts an electric field induced phase change refrigeration method of quickly adding an electric field and slowly removing the electric field; in different rows and columns, refrigeration sheets of the same layer or refrigeration sheets of every other layer work in the same manner, and the electric field adding (removing) work of the refrigeration sheets of each layer have a specific time sequence and cycle; and the ferroelectric stack arrays work alternately.
The Chinese patent CN201320028572.1 discloses a miniature refrigerator, including a refrigeration medium layer used for absorbing or releasing heat under the action of an electric field; the refrigeration medium layer is provided with a heat absorption end and a heat release end; a radiator used for releasing heat is connected with the heat absorption end of the refrigeration medium layer and a first heat switch for carrying out one-way heat transfer on the refrigeration medium layer through certain refrigeration equipment; a second heat switch for carrying out one-way heat transfer on the radiator through the refrigeration medium layer is located between the eat release end of the refrigeration medium layer and the radiator; and a heat isolation layer is covered on the peripheral outer surfaces of the refrigeration medium layer, the first heat switch and the second heat switch. The refrigerator is only suitable for local refrigeration of micro electromechanical equipment, and a refrigerator which reduces the temperature of a machining area by the electrocaloric effect is not involved in large equipment of machining such as grinding.
The Chinese Patent CN201310059826.0 discloses a heat pipe grinding wheel for dry grinding a difficult-to-machine material and a manufacturing method thereof, wherein the heat pipe grinding wheel includes a body and abrasive particles arranged on the body, and the body includes a base and an end cover; the abrasive particles are arranged on the end cover, and solid lubricants are coated on the abrasive particles; a heat pipe cavity is further formed between the end cover and the base, a degassing hole is formed on the base, and the degassing hole is communicated with the heat pipe cavity; a plug hole is formed at the outside of the degassing hole, and an inner plug and an outer plate, which are coaxially arranged, are arranged in the plug hole; a working medium is arranged in the heat pipe cavity; and condensate tanks are arranged on the outer surface located at a condensation segment of the heat pipe cavity of the end cover at intervals. The present invention can effectively disperse the heat in the cambered grinding area and can solve the bottleneck problem that the cooling liquid is unlikely to enter the cambered grinding area to effectively exchange heat.
The Chinese Patent CN201410707834.6 discloses a heat pipe grinding wheel for forming grinding, a heat pipe cavity is arranged in the grinding wheel, a working medium is filled in the heat pipe cavity, the inner wall surface of an evaporation end is close to a grinding surface of the grinding wheel, and a condensation end is away from the grinding surface of the grinding wheel; an independent vacuumizing interface and an endcapping interface are arranged on the end face of the grinding wheel, the vacuumizing interface is connected with a vacuumizing and liquid injecting device, the endcapping interface includes three channels, one channel is communicated with the external atmosphere, one channel is communicated with the vacuumizing interface through a degassing groove located in the grinding wheel, one channel is communicated with the heat pipe cavity through a degassing hole, the endcapping interface is matched with an endcapping module, after the endcapping module is installed, the endcapping interface is isolated from the external atmosphere, and the endcapping module controls the on-off of the degassing groove and the degassing hole in depth. The existing heat pipe grinding wheel has a good effect of reducing the temperature of the grinding area, but considering the heat exchange problem of the equipment cooperatively used with the grinding wheel for reducing the temperature of the grinding area, the structure of the heat pipe grinding wheel can be further improved.